In aircraft jet engines, a considerable portion of the noise is generated when the exhaust-gas stream exiting from the exhaust-gas nozzle at a high velocity mixes with the ambient air or, in the case of fanjet engines, when the primary-gas stream exiting from a gas turbine mixes with the secondary-gas stream accelerated by the fan, and also when the secondary-gas stream mixes with the ambient air. Since the noise increases by a power of about six to eight relative to the velocity of the gas stream, a reduction in the relative velocity between the adjacent interacting gas streams can significantly reduce the level of noise.
U.S. Pat. Appln. No. 2012/0186224 A1 discloses a system for noise reduction in which several outlet openings distributed along the circumference are used to blow out compressed air downstream from the gas outlet nozzle between adjacent, interacting gas streams.